Table of Contents

The Solar System
Planetary Data
Formation Theory Parameters
Magnetic Fields
Angular Momentum
Solar System Formation

Intro to Astronomy

Equitorial Coordinates
Understanding the Seasons

Time & Its Measurement


Solar & Lunar Eclipses


The Earth

The Moon

Mecury, Venus, Mars

The Outer Planets

Solar System Debris

The Sun

Evolution of Stars

Intersteller Matter

Sky Literacy

A Possible Sequence of Events for the Formation of the Solar System

  1. Gas and dust nebula collapses:
    1. Time: Began about five billion years ago
    2. Duration: 10 million years
    3. An interstellar cloud of gas and dust, approximately 50,000 AU in diameter, began to collapse gravitationally. Its mass may have been a few thousand solar masses. The cloud fragmented and one area with at least 1.1 to 2.0 solar masses, continued to collapse. Several mechanisms could have initiated such an event.
      1. Collection of mass from the explosion of a supernova. As the shock wave from the supernova event moves through space a region of higher density is generated immediately in back of the wave front.
      2. Magnetic fields which originate in the center of a galaxy give rise to shock fronts which move through the medium at lower velocities than the medium itself. As charged particles come in contact with the field lines, they are slowed, collecting matter which creates the necessary densities which generate stars.
      3. O B Associations: Hot luminous blue supergiant stars create interstellar winds from their tremendous outpourings of radiation which compress new material to form new stars, etc. This occurs in large, interstellar clouds of hydrogen.
  2. Pressure and density increased. Rotation of the nebula increased. The cloud formed a disk about 60 AU across and about one AU thick. Temperatures rose more rapidly near the center where the density and opacity were greatest. The center of the cloud may have been about 2000 K (3000 F), while the edge remained cold at about 100 K (-300 F). Dust vaporized near the center, and atoms became ionized creating a magnetic field which permeated the contracting mass.
  3. Transfer of angular momentum
    1. Duration: Perhaps as short as a few thousand years
    2. Magnetohydrodynamic effect transfers the sun's spin away from the inner to the outer solar system (Alfven-1954).
      1. Early contracting sun had a strong magnetic field.
      2. Area immediately surrounding the sun was composed of ionized particles. Charged particles interacted with the magnetic field so that they spiraled outward along the magnetic lines of force. These magnetic lines returned to the sun, trapping the ions.
      3. The sun was rotating faster than the ions in its vicinity.
      4. The magnetic field lines of the sun, sweeping through the ions tended to accelerate the cloud, increasing its rotational velocity at the expense of the sun's spin. Angular momentum was transferred away from the sun.
      5. The drag effect of the cloud against the sun also tended to decrease the rotational velocity of the sun.
      6. Differences in composition between the inner and outer planets can be accounted for.
        1. The magnetic field of the sun tended to cause more positively charged ions (especially the volatiles) to orbit around the forming star, thus helping to segregate the volatiles from the more refractory materials which condensed first in the cooling nebula. The condensed refractories such as iron, nickel, and silicate grains would no longer have been affected by the solar magnetic field, because they would have been neutral. This matter would have collected into the more refractory terrestrial planets, i.e., the inner solar system.
        2. The volatiles would have remained charged and thus they would have been affected by the sun's magnetic field. These materials would have spiraled away from the sun along the sun's magnetic field lines and condensed much farther away in the cooler regions where the Jovian planets orbit the sun today.
      7. The basic problem of the Magnetohydrodynamic Effect lies with the assumption that the sun's magnetic field strength would have had to have been 150,000 times stronger than it is today. Presently the field strength of the sun is approximately two gauss, four to six times that of the earth's field strength.
  4. Formation of grains and planetesimals
    1. Grains condensed with the composition dependent upon the temperature of the immediate environment. Generally, the denser terrestrial materials formed nearer to the sun, while icy materials condensed farther away.
    2. Grains collided to form planetesimals, small bodies ranging in size from millimeters to 10 kilometers. They grew through direct physical collisions with each other.
  5. Evolution of the planets from protoplanets
    1. Planetesimals became protoplanets once their masses became great enough to possess an effective gravitational field. The ability of protoplanets to obtain more mass was not limited strictly to their cross sectional areas, as it was for planetesimals. At this point the protoplanet population rapidly assembled into the solar system as we essentially know it today.
    2. The sun initiates thermonuclear fusion. Solar wind and radiation swept out the remaining gaseous materials from the nebular disk.
    3. The inner planets became heated and melted. Their primordial atmospheres were lost. Outgassing from these bodies through volcanic eruptions eventually created secondary atmospheres. The Jovian planets because of their great masses retained their primeval atmospheres which are similar to the composition of the present-day sun.